Traditionally, the failure to remove residue in the gap of ink jet printheads that have a drop generator, orifice plate secured to the orifice plate forming a jet array, and a charge plate disposed opposite the orifice plate has resulted in operating error, such as an electrical short to the charge plate. Eventually, ink or other residue build-up can shorten printhead life or otherwise result in high maintenance costs caused by expenses for replacement parts and corresponding labor costs.
While a printhead shutdown sequence can remove the bulk of the liquid such as ink, from an ink jet printhead, some ink residue may be left on the exterior of the orifice plate and on the face of the charge plate. Such residues can result in misdirected jets or to specific electrical shorts between charging electrodes on the charge plate face. A need has existed for a method to remove such ink and other residues before using the printhead.
Startup processes or sequences that clear ink from printheads are taught in U.S. Pat. Nos. 4,591,870 and 4,591,873 that are incorporated by reference. These methodologies remove ink residues and to prepare the printhead for printing but these methodologies have not have the ability to be used on a continuous basis and only during startup. A need exists for other methods that can be used continuously with printhead use
A need exists for an improved method of removing residue from an ink jet printhead during cross flush prior to and during the establishment of the continuous ink jet array to effectively clear the fluid, such as ink, from the gap between the orifice plate and the charge plate.
A specific need exists for 110 kHz 9-inch printheads operating with the high surface tension color inks (but not limited to those inks) for failures relating to “segment over current.” These printheads have shown, over time, damage to the top surface of the charge plate coating and subsequent charge plate circuitry in the wetted footprint projected area of the orifice plate. “Segment over current” errors apparently occurred when excessive current was detected through any one or more of the 18-voltage segments comprised of the 42 IC chips. If charge plate circuitry is exposed to ink when charge voltage is applied, a high current draw will be detected and a “segment overcurrent” error will be displayed. This phenomenon occurs in the wetted area between the orifice plate and charge plate gap due to ink left in this area because of the breakdown of the dielectric strength of the charge plate coating thereby resulting in errors in the future. Accordingly, the present methods and systems were developed to address this specific problem.
Most situations of ink in the gap between the orifice plate and the charge plate have been cleared after first weeping ink in a cross flush state by closing the fluid outlet from the drop generator or a cross flush valve after the drop generator to create a water hammer pressure pulse that establishes the jets and pulls the excessive ink out of the gap. This method has problems in that the ink jet curtain is established too quickly to remove the ink effectively from the gap. A new method has been needed to slow the formation of the ink jet curtain to allow more time to clear the ink from the gap.
The present embodiments described herein were designed to meet these needs.